A firearm scope typically includes a series of lenses which produce an image of a target object inside the scope at multiple locations or “focal planes” within the scope. These lenses are positioned very precisely within a tubular structure that mounts atop a firearm. Scopes typically include a sighting aid which can be as simple as a cross hair reticle having two intersecting fibers mounted within a ring that is placed on a longitudinal axis of the tube. The cross hairs are located on one of the focal planes formed by the lenses so as to be superimposed on an image of the target.
A shooter looks through one or more ocular lenses within an eyepiece at the rear of the scope, and it is this eyepiece that focuses and magnifies the final image for the shooter. Specifically, the position of the eyepiece or ocular lens system is typically adjustable within the rear of the scope to allow a shooter to correct the focus to conform to the shooter's own vision shortcoming, be it myopia or hyperopia (nearsightedness or farsightedness, respectively). The focus adjustment is commonly referred to as a diopter adjustment, since myopia is measured in “diopters.”
The rearmost portion of this adjustable ocular lens mount is frequently cushioned and commonly referred to as an “eyecup.” However, unlike other optical systems (e.g., telescopes or binoculars), a firearm scope should not be placed directly against a shooter's eye due to the risk of injury resulting from recoil. Therefore, firearm scope optics are designed such that a user's eye must be positioned within a focal plane approximately 3 to 5 inches rearward of the last ocular lens within the scope. This rearmost focal plane typically provides a shooter about 0.5 to 1.0 inches of latitude to move fore and aft while still maintaining a full field of view.
The distance from the rearmost ocular lens within the eyepiece and the shooter's eyeball is typically referred to as “eye relief.” FIG. 1 graphically illustrates this distance by the arrow 20 labeled “Eye Relief.” As noted above and described in greater detail below, an eye relief of several inches is necessary to provide a buffer against the recoil associated with shooting a firearm. Firearm scopes are designed to balance a variety of competing interests, including eye relief, magnification, and field of view (observable area). In fact, there is a three-way tradeoff such that the field of view supplied by a given magnification is decreased as eye relief is increased. Similarly, for a given field of view, an increase in eye relief results in a decrease in magnification. Hunters often place a premium on both field of view and magnification, frequently at the expense of eye relief.
While “eye relief” represents the distance from the rear surface of the ocular lens to the shooter's eyeball, the clearance between the eyecup (i.e., the rearmost portion of the scope) and the shooter's face is referred to as “eye clearance.” Eye clearance, then, is a function of eye relief though it is less rigidly defined and varies with the construction of the firearm scope and the stance a shooter uses to hold the firearm. FIG. 1 includes an arrow 22 graphically illustrating one example of “eye clearance” between an eyecup 24 and a portion of the shooter's face, although this dimension is not restricted to any specific area of the face and will vary with facial structure and positioning. Thus, eye clearance can be thought of as the shortest distance from the eyecup to that part of the shooter's face that is first struck if the scope moves far enough rearward during recoil.
Given the competing requirements noted above, firearm scope designs are a compromise that yield less than ideal eye clearance in some situations. Consequently, a recurrent problem experienced by firearm scope users is an injury to the eye area induced by impact of the eyecup with the shooter's face during recoil. Additionally, sufficient eye clearance obtained when a shooter holds the firearm comfortably with the head in a natural position may not be enough when a shot is taken while aiming uphill or on uneven ground. Furthermore, even experienced shooters may suffer an injury when the recoil from an unfamiliar gun is greater than anticipated. Indeed, the current trend toward more powerful firearms and cartridges has increased the incidence of bodily injury and thus there is a need for more eye clearance than current designs allow.
Some firearm scopes utilize cushion devices or elastomeric bellows attached to the eyecup to cushion a potential impact between the scope and a shooter's face. However, a common failing of such existing devices is that they add length to the rear end of the scope, thereby reducing eye clearance and placing the shooter's face closer to the eyecup which causes injury. That is, the addition of a cushioning device to the eyecup of a scope does not alter the “eye relief” (i.e., the distance to the ocular lens) but rather shortens the “clearance” distance between the shooter and the scope. FIG. 1 illustrates this problem by showing a relatively shorter clearance distance 30 between the shooter's face and a protective bellows 32 shown in phantom. Therefore, prior art cushioning solutions compel the shooter to place the scope near enough the eye to be of concern, particularly on high recoil guns.
Thus, there is a need to provide protection to firearm users without reducing the eye clearance provided by a scope.